The invention relates to a hybrid drive for a hybrid vehicle.
Hybrid drives are used in modern motor vehicles, wherein, for example, an internal combustion engine and an electric motor are provided in the drivetrain of a vehicle. Here, it is sought to operate the engine and motor as efficiently as possible.
It is an object of the invention to specify an improved hybrid drive for a hybrid vehicle.
This and other objects are achieved by way of a hybrid drive for a hybrid vehicle, including an internal combustion engine which has a crankshaft, and including an electric motor, wherein the electric motor is coupled to the crankshaft of the internal combustion engine by way of an automatically shifting transmission, according to embodiments of the invention.
For example, the electric motor provides, in a simple manner, the starting functionality for the internal combustion engine, and said electric motor can furthermore be operated as a generator. Accordingly, the electric motor can assist the run-up of the crank drive or of the crankshaft, in order to realize as smooth and excitation-free a run-up as possible. Above a certain rotational speed of the internal combustion engine, the electric motor can be switched into the generator mode, and can itself be driven by the internal combustion engine.
Regulated motor operation of the electric motor is preferably implemented.
In particular, the electric motor may be designed to realize all starting requirements, in particular low-temperature starts of the internal combustion engine.
The electric motor may serve for permitting automatic starting and stopping, in the case of which the internal combustion engine must be shut down and reactivated after a certain period of time. This may be after the vehicle comes to a standstill, for example at a traffic signal, though may also be during coasting, that is to say when the vehicle is rolling without being driven by the internal combustion engine. The starting of the internal combustion engine must in this case satisfy extremely high demands with regard to comfort.
The hybrid drive may be such that, downstream of the internal combustion engine, there are connected a system for compensating the rotational speed non-uniformity of the crankshaft, a characteristic converter, and a multi-gear-ratio vehicle transmission, for the purposes of transmitting the power of the internal combustion engine to wheels, which are to be driven, of a vehicle. In this way, an efficient and as far as possible excitation-free transmission of power to the wheels of the vehicle to be driven is possible. It is self-evident that further components, such as for example a differential, may be incorporated into the drivetrain.
The vehicle transmission may be an automatic transmission or a manually shiftable transmission. In particular, it is thus possible for inexpensive and reliable manually shiftable transmissions to be incorporated into the hybrid drive and combined with the internal combustion engine and electric motor in a modular system. In this way, cost advantages are obtained in relation to already known hybrid solutions, because extensively tested and inexpensive manual shift transmissions can be used. Alternatively, automatic transmissions such as those installed in conventional vehicles with an internal combustion engine may be used.
In one refinement of the hybrid drive, a further electric motor is incorporated between the characteristic converter and the vehicle transmission. The additional electric motor may serve for electric driving, electric crawling and the recuperation of braking energy, or else for “boosting” when the internal combustion engine is at a standstill.
The internal combustion engine may be arranged coaxially or axially parallel with respect to a transmission input shaft of the vehicle transmission, such that, in accordance with the available structural space, the electric motor can be positioned optimally in a vehicle.
The use of two electric motors in a hybrid drive has the advantage that the hybrid functions relating to the internal combustion engine and the hybrid functions relating to the drive or vehicle transmission can be divided between two separate electric motors, such that said motors can each be optimally dimensioned with regard to their intended functionality in the drivetrain.
The additional electric motor may in particular be couplable via a transmission to the transmission input shaft of the vehicle transmission, in order to operate the electric motor as efficiently as possible.
The automatically shifting transmission assigned to the electric motor relating to the internal combustion engine may, in one refinement of the hybrid drive, have a planetary transmission. By way of the planetary transmission, even high transmission ratios can be provided in a compact manner.
Alternatively or in addition, the automatically shifting transmission may have shift elements which are actuable by way of an actuator, wherein the actuator is in particular controllable by a control unit.
For example, the control unit may actuate the actuator in a manner dependent on an operating parameter in the drivetrain, in particular the rotational speed of the internal combustion engine or the like, in order to effect a gear ratio change in the automatically shifting transmission.
It is thus possible in particular for a gear ratio change in the automatically shifting transmission, and a switch from the motor mode to the generator mode, to be performed as soon as a rotational speed of the internal combustion engine predefined in the control unit is exceeded during the run-up of the crank drive. Such functionality is preferably implemented fully automatically, without any action on the part of the driver.
In a further refinement of the hybrid drive, the planetary transmission has an internal gear, which is assigned a first freewheel, and a sun gear, which is assigned a second freewheel. The freewheels serve for permitting a switch of the electric motor from the motor mode to the generator mode, wherein a reversal of the torque flow from the internal combustion engine to the electric motor is made possible by way of the freewheels.
The input and output of drive may be realized via the sun gear and via a planet carrier of the planetary transmission in the motor mode of the electric motor.
The input and output of drive may be realized with static planet gears of the planetary transmission in the generator mode.
The automatically shifting transmission may have an output shaft which may be coupled in particular via a gearwheel pairing to the crankshaft of the internal combustion engine. In this way, the electric motor can be connected into the hybrid drive in a compact manner, wherein an additional transmission ratio can be provided by way of the gearwheel pairing.
The gearwheel pairing may be a spur-gear stage, wherein it is possible in an inexpensive manner to use known toothings.
In order to take up as little structural space as possible, it may be provided that the automatically shifting transmission is a transverse transmission.
In a further refinement, the hybrid drive is characterized in that a first gear ratio of the automatically shifting transmission has a transmission ratio in a range from 1.5 to 2.5, in particular from 1.7 to 2.3, preferably from 1.9 to 2.1, and a second gear ratio of the automatically shifting transmission has a transmission ratio in a range from 3.5 to 4.5, in particular from 3.7 to 4.3, preferably from 3.9 to 4.1.
For example, the transmission ratio of the first gear ratio may be equal to 2, and the transmission ratio of the second gear ratio may be equal to four.
In the present case, a transmission ratio of four means that an input rotational speed introduced into the automatically shifting transmission at the electric motor side is converted by way of the transmission into an output rotational speed in accordance with the specification i=4=input rotational speed/output rotational speed.
Here, the first gear ratio may serve for the generator mode, and the second gear ratio may serve for the motor mode. The lower transmission ratio for the generator mode ensures that the electric motor is not overloaded even during the run-down of the internal combustion engine.
It is self-evident that the above-mentioned transmission ratios represent the overall transmission ratio for the automatically shifting transmission. For example, if a planetary transmission is combined with a spur-gear stage, wherein the spur-gear stage serves for the connection of the transmission to the crankshaft, the overall transmission ratio is defined by the transmission ratio of the spur-gear stage and the transmission ratio of the respective gear ratio of the planetary transmission.
To realize a reliable and practical embodiment of the automatically shifting transmission, the transmission ratio of the second gear ratio may correspond at least to 1.5 times, in particular at least two times, the transmission ratio of the first gear ratio.
The spur-gear stage may have a transmission ratio in a range from 1.5 to 2.5. In particular, the transmission ratio of the spur-gear stage may be equal to 2.
The planetary transmission may have a transmission ratio of 1 in the first gear ratio, and a transmission ratio in a range from 1.5 to 2.5, in particular from 1.7 to 2.3, preferably from 1.9 to 2.1, in the second gear ratio.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.